It is the simple form of a surge protection device. It has one power capacitor in series with a resistor. Like other surge protection devices, it is also connected between the line and earth of the system.
Functions of Capacitance Resistance Type Surge Suppressor
Whenever there is a current chopping in the system an inductive overvoltage may arise. The voltage rises in the system due to the inductance available in the system. The capacitance of the capacitance-resistance type surge arrester or surge capacitor balances this inductance and therefore reduces the transient voltage during switching operation. The equation given below gives a clear concept of the matter.
The resistance of the resistor connected in series with the capacitor dissipates the surge energy. Therefore it facilitates the reduction in multiple traveling of the surge wave in the system.
The capacitive effect of the device also helps to reduce the rising rate of the voltage appearing between the contacts ab circuit breaker after the interruption of currents. Therefore ultimately it reduces the chances of occurrence of reionization during opening the breaker contacts.
The capacitance resistance type surge suppressors and surge capacitor reduce the high-frequency current exponentially depending on the time constant of the CR circuit of the device.
Since the device helps to reduce the reionization between the contacts of circuit breakers, it virtually reduces the chances of current chopping in the system during switching operation.
Also, it reduces the transient overvoltage in the system during making operations of circuit breakers.
Calculation of Capacitance in Capacitance Resistance Type Surge Suppressor
We can calculate the value of the capacitance by using the below-mentioned equation.
Here is the load inductance or the inductance of the system. C is the capacitance of the device.
Also, there are some experimental standard values of capacitance as well as series resistance for using the device for the specific system voltage. The capacitance value of 0.04 microfarads to 0.3 microfarads and the resistance value of 20 ohms to 1000 ohms are suitable for use in the medium-voltage system.